Porous inorganic membranes and method of manufacture

ABSTRACT

A method is provided for making a porous inorganic membrane by using a mixture of an inorganic material, organic polymer particles and a solvent to form a slurry, the particles being non-spherical, distributing the slurry onto a surface, drying the slurry to remove the solvent and firing the dried slurry to produce the porous inorganic membrane. Examples of organic polymer particles include particles of acrylic. A substrate with a porous inorganic membrane disposed on the substrate is also provided, the inorganic membrane having an average thickness of from about 0.5 micron to about 30 microns, a porosity of from about 30% to about 65%, a median pore size (d50) of from about 0.01 micron to about 1 micron, and a value of (d90−d10)/d50 less than about 2, as measured by mercury porosimetry. An example of a substrate includes an inorganic porous support.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. Provisional Application Ser. No. 61/349,357, filed on May 28, 2010,the content of which is relied upon and incorporated herein by referencein its entirety.

BACKGROUND

The present disclosure relates generally to porous inorganic membranesand methods for preparing inorganic membranes and coatings, andparticularly to porous inorganic membranes and coatings having uniformpore size distribution.

Porous inorganic membranes have been widely used for industrial liquidfiltration, and have recently been investigated for gas-particulateseparations, pervaporation (combination of membrane permeation andevaporation), gas separations and catalytic reactions.

In known coatings currently available, the pore structures are generallyformed from particle packing during drying and firing process. Thisresults in limited porosity and variation in the pore size distribution.

SUMMARY

In one aspect, the present disclosure provides a method for making aporous inorganic membrane comprising the steps of mixing an inorganicmaterial, organic polymer particles (such as acrylic, e.g in the form ofan acrylic emulsion, and the acrylic emulsion comprises acrylicparticles) and a solvent to form a slurry, the particles beingnon-spherical, distributing the slurry onto a surface, drying the slurryto remove the solvent and firing the dried slurry to produce the porousinorganic membrane.

In another aspect, the present disclosure provides a method forproducing a porous support with a porous inorganic coating comprisingthe steps of mixing an inorganic material, an acrylic emulsion and asolvent to form a slurry, wherein the acrylic emulsion comprises acrylicparticles, the particles being non-spherical, coating the porous supportwith the slurry, drying the slurry on the porous support to remove thesolvent and firing the dried slurry on the porous support to produce theporous support with the porous inorganic coating. In another aspect, asubstrate with a porous inorganic membrane disposed on the substrate isdisclosed herein, the inorganic membrane having an average thickness offrom about 0.5 micron to about 30 microns, and in some embodiments fromabout 1 micron to about 10 microns, a porosity of from about 30% toabout 65%, a median pore size (d50) of from about 0.01 micron to about 1micron, and a value of (d90−d10)/d50 less than about 2, as measured bymercury porosimetry; the substrate may be an inorganic porous support.Thus, present disclosure provides a porous inorganic membrane having ahigh porosity and uniform pore size distribution, as well as pore size,to help provide better separation efficiency, and/or better permeabilityand thus low backpressure.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention, and are incorporated into and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention, and together with the description serve to explain theprinciples and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the particle size distribution of pore formersand alumina;

FIG. 2 is a graph showing the pore size distribution of an aluminamembrane without the addition of a pore former;

FIG. 3 is a scanning electron micrograph image of the surface morphologyof the alumina membrane of FIG. 2;

FIG. 4 is a graph showing the porosity of an alumina membrane as afunction of the amount of a spherical pore former;

FIG. 5 is a graph showing the pore size distribution of aluminamembranes made with and without a spherical pore former;

FIG. 6A is a scanning electron micrograph image of the surfacemorphology of an alumina membrane without the addition of a pore former;

FIG. 6B is a scanning electron micrograph image of the surfacemorphology of an alumina membrane made with 20 vol % of a spherical poreformer;

FIG. 6C is a scanning electron micrograph image of the surfacemorphology of an alumina membrane made with 40 vol % of a spherical poreformer;

FIG. 6D is a scanning electron micrograph image of the surfacemorphology of an alumina membrane made with 60 vol % of a spherical poreformer;

FIG. 7 is a graph showing the porosity of an alumina membrane as afunction of the amount of a non-spherical pore former;

FIG. 8 is a graph showing the pore size distribution of aluminamembranes made with and without a non-spherical pore former;

FIG. 9A is a scanning electron micrograph image of the surfacemorphology of an alumina membrane without the addition of a pore former;

FIG. 9B is a scanning electron micrograph image of the surfacemorphology of an alumina membrane with made 20 vol % of a non-sphericalpore former;

FIG. 9C is a scanning electron micrograph image of the surfacemorphology of an alumina membrane made with 40 vol % of a non-sphericalpore former;

FIG. 9D is a scanning electron micrograph image of the surfacemorphology of an alumina membrane made with 60 vol % of a non-sphericalpore former;

FIG. 10 A is scanning electron micrograph image of the surfacemorphology of a cordierite membrane with a non-spherical pore former;

FIG. 10B is a scanning electron micrograph image of the surfacemorphology of a cordierite membrane without a pore former; and

FIG. 11 is a graph showing the pore size distribution of a cordieritemembrane with a non-spherical pore former.

DETAILED DESCRIPTION

Broadly, a method is disclosed herein for making a porous inorganicmembrane that, for example, can be used in liquid filtration, gasseparation, diesel particulate filters or gasoline particulate filters.The method for making the porous inorganic membrane may comprise thesteps of mixing an inorganic material, organic polymer particles (suchas an acrylic in the form of an acrylic emulsion) and a solvent to forma slurry. The slurry may be distributed onto a surface and dried toremove the solvent. The dried slurry may then be fired to produce theporous inorganic membrane. The acrylic emulsion may comprise acrylicpolymers that act as pore formers. The acrylic emulsion may be used apore former and may comprise acrylic polymers. The organic polymerparticles, such as acrylic polymers, may be spherical or non-spherical.The porous inorganic membrane may be distributed onto a porous supportto form a thin coating on that support. The use of organic polymerparticles such as acrylic polymers as pore formers allows for controlledpore size distribution. The distribution may either by single modal orbi-modal.

In some presently disclosed embodiments, an acrylic emulsion comprisingacrylic polymers may be used as a pore former. The acrylic emulsion maycomprise acrylic polymers where the acrylic polymers are eitherspherical or non-spherical in shape. A non-limiting example of anacrylic emulsion having spherical acrylic polymers is RHOPLEX™ B-85acrylic emulsion (Dow Chemical Co.). In some embodiments the acrylicpolymers are non-spherical in shape. A non-limiting example of anacrylic polymer that is non-spherical is a multi-lobed acrylic polymer.Multi-lobed acrylic polymers are well known in the art and commerciallyavailable. RHOPLEX™ MULTILOBE™-400 acrylic binder (Dow Chemical Co.) isone example of a multi-lobed acrylic polymer. The number of lobes of themulti-lobed acrylic polymer may be from at least 2. In some embodiments,the number of lobes may be from about 2 to about 8. Other embodiments ofnon-spherical pore formers include materials that are decomposed byoxidation, such as organic polymers like cellulosic, styrene, urethane,and polyolefin structures, as well as activated carbon, andnon-activated carbon. A non-spherical pore former can comprisenon-spherical pore former particles comprising a first plurality ofco-planar lobes or arms, and may optionally include one or more lobes orarms which are not coplanar with the first plurality of co-planar lobesor arms; thus, in some embodiments, the centers of each of the firstplurality of co-planar lobes or arms lie substantially in a first plane,and the centers of one or more lobes or arms substantially outside thefirst plane; in some embodiments, the non-spherical pore formercomprises non-spherical pore former particles, each particle havinglobes or arms that are disposed in a common plane. While not wishing tobe bound by theory, it is believed that the multi-lobed acrylic polymersincrease the porosity of a porous inorganic membrane with a single modalpore distribution because the lobes, or arms, of the polymer may touchand therefore, after being burned out, connect the pores together.

The amount of acrylic emulsion in the slurry may be from about 10 vol %to about 80 vol % of total inorganic solids and polymers. Alternatively,the amount of acrylic emulsion in the slurry may be from about 20 vol %to about 60 vol % of total inorganic solids and polymers. The amount ofboth the spherical and non-spherical acrylic polymer emulsions arelinearly proportional to the porosity of the porous inorganic membrane.However, the spherical and non-spherical acrylic polymers differ in poresize distribution. At low concentrations, both the spherical andnon-spherical have a single modal pore size distribution. However, asthe concentration of increases, the spherical acrylic polymer produces aporous inorganic membrane having a bi-modal pore size distribution,while the non-spherical remains single modal. In some embodiments theporous inorganic membrane has a pore size distribution as measured bymercury porosimetry comprising a mono-modal distribution wherein(d90−d10)/d50 is less than about 2 and the pores having a size of d90 orless comprise about 90% of the total pore volume, the pores having asize of d50 or less comprise about 50% of the total pore volume and thepores having a size of d10 or less comprise about 10% of the total porevolume.

In some presently disclosed embodiments, the inorganic materials can beany combination of inorganic components that, upon firing, can provide aprimary sintered phase composition. The inorganic ceramic-formingingredients may be cordierite, mullite, clay, talc, zircon, zirconia,spinel, aluminas and their precursors, silicas and their precursors,silicates, aluminates, lithium aluminosilicates, feldspar, titania,fused silica, nitrides, carbides, borides, e.g., silicon carbide,silicon nitride, soda lime, aluminosilicate (such as zeolite),borosilicate, soda barium borosilicate or combinations of these, as wellas others. Combinations of these materials may be physical or chemicalcombinations, for example, mixtures or composites, respectively. In someembodiments, the inorganic material may be alumina or cordierite. Theinorganic material and the acrylic emulsion may be mixed together with asolvent to form a slurry. The solvent may be aqueous based, which maynormally be water or water-miscible solvents, or organically based.Typically, the amount of aqueous solvent is from about 50% by weight toabout 95% by weight. The slurry may also comprise additional materialssuch as, but not limited to, a dispersant, a binder, an anti-crackingagent, an anti-foaming agent, or combinations thereof.

In other embodiments presently disclosed, the method comprisesdistributing the slurry onto a surface. The surface may be a temporarytemplate form where the porous organic membrane is removed before use,or it may be a support where the slurry is coated onto the surface ofthe support. Temporary templates may be any material that allows for thefacile removal of the porous inorganic membrane from the template.Non-limiting examples may be plastic or glass, such as petri dishes. Thesupports to be coated may comprise any desired material that the porousinorganic membrane will bind to, such as porous ceramics. In someembodiments, the porous support may be a ceramic comprising cordierite,alpha-alumina, mullite, aluminum titinate, titania, zirconia, ceria orcombinations thereof. The support may have convenient size and shape,depending on the use of the coated support. In some embodiments, thesupport is a honeycomb monolith, which may be used in any number ofapplications, such as catalytic, adsorption, electrically heatedcatalyst, filters such as diesel particulate filters, molten metalfilters, etc.

The slurry may be distributed onto the surface by any means known in theart including, but not limited to, dip coating, pouring or spraying. Insome embodiments, the support may be submerged in the slurry, removed,and drained of excess slurry. After the slurry is deposited onto thesurface, the slurry is dried to remove the solvent. The slurry may bedried under ambient temperature and humidity. Alternatively, heat may beapplied to dry the slurry. In some embodiments, the slurry is dried at atemperature of from about 25° C. to about 120° C. If desired, the slurrymay be dried under conditions where the atmosphere and humidity arecontrolled. In some embodiments, the slurry may be dried in anenvironment of air or nitrogen gas at a humidity of from about 60% to90%. The increased humidity allows the solvent to be removed, butinhibits cracking and spalling of the slurry. If the slurry isdistributed onto a temporary template, it may be removed after dryingbut before firing.

After drying, the slurry may be fired to form the final porous inorganicmembrane. Firing of the dried slurry hardens the membrane and alsoremoves the acrylic polymer pore former, resulting in a porous membrane.Firing conditions are well known in the art and the skilled artisan candetermine the correct conditions for the porous inorganic membrane beingmade without undue experimentation. In some embodiments, the driedslurry is fired for about 20 hours to about 45 hours at a temperature ofabout 1100° C. to about 1400° C.

The porous inorganic membrane may be selected based on properties ofboth support and membrane material. If the porous inorganic membrane isbeing applied to a porous support having a plurality of channels, suchas with a honeycomb monolith, a thin membrane may be preferred to avoidpotential cracking issues. In some embodiments, the thickness may befrom about 0.5 micron to about 30 microns. The thickness of the membraneis controlled by the amount of slurry distributed onto the surface. Thethickness may also depend on the surface or support used. If the porousinorganic membrane is being applied to a porous support have a pluralityof channels, such as with a honeycomb monolith, a thin coating may bepreferred so as not to block any channels. Alternatively, if the porousinorganic membrane is to be free standing, a thicker membrane may bedesired for ease of handling. In some embodiments, the thickness may befrom about 1 micron to about 10 microns.

The porosity of the porous inorganic membrane may be controlled by theamount of acrylic emulsion that is added to the slurry. As there is alinear relationship between the amount of acrylic emulsion added and thefinal porosity, the amount of acrylic emulsion required to give thedesired porosity may be calculated without undue experimentation. Insome embodiments, the porous inorganic membrane has a porosity of fromabout 20% to about 80% or, alternatively, a porosity of from about 30%to about 65%.

EXAMPLES

The following non-limiting examples are provided for furtherillustration.

Example 1 Deposition of Porous Alumina Membranes without Use of PoreFormer

An alumina slurry comprised of 8 wt. % alumina was made by mixingalumina, Tiron and deionized water. The alumina was AKP30 from SumitomoChemical with a mean particle size of 0.2-0.3 μm. The particle sizedistribution as measured by a Nanotrac Particle Size Analyzer (MicrotracInc., Montgomeryville, Pa.) is shown in the line connecting the solidcircles in FIG. 1. Tiron (4,5-Dihydrony-1,3-benzenedissulfonic aciddisodium salt) was used as a dispersant. 0.018 g of Tiron was added in abeaker containing 69 g of deionized water. When the Tiron was completelydissolved, 60 g of alumina was added. After ball-milling overnight, theslurry was poured through a fine screen, followed by degassing for 1hour with a vacuum pump.

The alumina slurry was poured down into a Petri dish. After drying at120° C. overnight, the resulted cake layer was scratched off the dish,and fired at 1150° C. for 2 h with a heating and cooling rate of 1° C.per minute.

The fired unsupported alumina membrane was characterized by Hgporosimetry and scanning electron microscopy (SEM). FIG. 2 shows asingle modal pore size distribution of the alumina membrane with amedian pore size of 0.11 um and porosity of 31.1%. FIG. 3 shows the SEMsurface morphology of alumina membrane. It can be seen that aluminaparticles are packed closely, giving rise to low porosity.

Example 2 Deposition of Porous Alumina Membranes with Use of a SphericalPore Former

This example describes deposition of unsupported porous alumina membraneusing different loadings of spherical acrylic emulsion particles as apore former. Rhoplex™ B-85 acrylic emulsion from Rohm and Haas (now DowChemical Co.) was used in this example. The solution contained 38%acrylic particles. The majority of particles were about 60-70 nm insize, which is consistent with particle size analysis result shown bythe line connecting the hollow triangles in FIG. 1.

Three alumina slurries were made containing 8 wt. % alumina and 20%, 40%and 60% of B-85 by volume by mixing alumina, Tiron, a B-85 solution anddeionized. water. To make the slurry containing 40% pore former, 0.018 gof Tiron was dissolved in 67.3 g of deionized water, followed by theaddition of 6 g of AKP30 alumina and 1.75 g of B-85 solution. Afterball-milling overnight, the slurry was screened and degassed. The volumeratio of B-85 acrylic particles to alumina particles was 40:60.

Three unsupported alumina membranes were prepared with the three aluminaslurries, respectively. The same procedure was used as in Example 1. Thedried membranes were fired at the same temperature of 1150° C. for 2 h.

FIG. 4 shows the porosity as a function of pore former content. A linearincrease in porosity was found with increasing pore former content. Theporosity was increased from 31% to 50% when 60 vol. % B-85 was used ascompared to the control.

FIG. 5 compares the pore size distribution of the alumina membranes madewith 0%, 20%, 40% and 60% pore former by volume. The membrane kept asingle modal pore size distribution when 20% B-85 was used, however, thepore size distribution became bi-modal with addition of 40% or more. Thevalue of (d90−d10)/d50 was 6.8 and 3.8 for the samples made with 40 vol% and 60 vol % of B-85, respectively.

FIGS. 6A-6D compare SEM images of surface morphology of the aluminamembranes made without (FIG. 6A) and with use of 20% (FIG. 6B), 40%(FIG. 6C), and 60% (FIG. 6D) by volume the pore former B-85. The aluminamembranes appeared more porous with addition of the pore former, withlarge pores being observed when 40% or more B-85 was used (FIGS. 6C and6D). This was consistent with Hg porosimetry data shown in FIG. 5.

Example 3 Deposition of Porous Alumina Membranes with Use of aNon-Spherical Pore Former

This example describes deposition of unsupported porous alumina membranemade with a non-spherical pore former. Rhoplex™ Multilobe™ 400 acrylicbinder from Rohm and Haas was used in this example. The solution controlcontained 53.0-54.0% solid. The majority of particles were about 300 nmin size, which is consistent with particle size analysis result shown bythe line connecting the hollow squares in FIG. 1.

Three alumina slurries containing 8 wt. % alumina and 20%, 40% and 60%Multilobe™ 400 by volume were prepared. As an example, to make theslurry containing 40% pore former, 0.018 g of Tiron was dissolved in68.2 g of deionized water, followed by the addition of 6 g of AKP30alumina and 1.25 g of Multilobe™ 400 solution. After ball-millingovernight, the slurry was screened and degassed. The volume ratio ofMultilobe™ 400 acrylic particles to alumina particles was 40:60.

Three unsupported alumina membranes were prepared with use of the threealumina slurries with the non-spherical pore former, respectively. Thesame procedure was used as in Example 1. The dried membranes were firedat the same temperature of 1150° C. for 2 h.

FIG. 7 shows the porosity as a function of pore former content. A linearincrease in porosity was found with increasing pore former content. Theporosity was increased from 31% to 49% when 60 vol. % of Multilobe™ 400was used.

FIG. 8 compares the pore size distribution of the alumina membranes madewith 0%, 20%, 40% and 60% non-spherical pore former by volume. Differentfrom the membranes prepared with B-85, the membranes in this examplekept a single modal pore size distribution when 60% pore formerMultilobe™ 400 was used. The value of (d90−d10)/d50 was 0.81 for boththe samples made with 40 vol % and 60 vol % of Multilobe™ 400.

FIGS. 9A-9D compare the SEM images of surface morphology of the aluminamembranes made without (FIG. 9A) and with use of 20% (FIG. 9B), 40%(FIG. 9C), and 60% (FIG. 9D) by volume of the pore former Multilobe™400. Uniform surface morphology and pore size were found with highloading of the pore former. This is consistent with Hg porosimetry datashown in FIG. 8.

Example 4 Deposition of Porous Cordierite Membranes with Use of AnotherPore Former

This example describes deposition of supported porous cordieritemembrane using the same pore former as in Example 3, Rhoplex™ Multilobe™400 acrylic binder.

The honeycomb monolith support used in this example was made ofcordierite with an outer diameter of 1 inch and a length of 2 inchcomprising 125 rounded channels of an average diameter of 2 mm beinguniformly distributed over the cross-sectional area. The support had amedian pore size of 3.8 μm and porosity of 45.7%, as measured by mercuryporosimetry. The support was flushed through the channels with deionizedwater, and was fully dried in a 120° C. oven overnight.

A cordierite slurry containing 15% by weight fine cordierite materialand 40% Multilobe™ 400 by volume was prepared. The volume ratio ofMultilobe™ 400 acrylic particles to cordierite particles is 40:60. Thefine cordierite has a median particle size (d50) of 1.9 um. 0.18 g ofTiron was dissolved in 319.4 g of deionized water, followed by theaddition of 33.45 g Multilobe™ 400 solution, 60 g of cordierite and 5.1g of DC-B anti-foam emulsion solution (Dow-Corning). After ball-millingovernight, the slurry was screened and degassed.

The cordierite membrane was placed inside the channels of the supportusing a flow-coater that was disclosed in U.S. Published PatentApplication 2008/0237919. The soaking time (contact time between theslurry and the support wall surface) was 20 seconds. After the slurrywas discharged, the coated support was spun for 60 seconds at a speed of525 rpm to remove excess cordierite slurry in the channels. Thesupported cordierite membrane was dried at 120° C. for 2 h under a N₂flow with a humidity of 60%, although drying in a stagnant air may be analternative. The dried membrane was fired at 1150° C. in air for 2 h ata heating rate of 1° C./min.

FIGS. 10A and 10B compare SEM images of the surface morphology of theresulted cordierite support with the cordierite membrane made of thesame cordierite material but made with the pore former Multilobe™ 400(FIG. 10A) and without the pore former (FIG. 10B). The surface of themembrane made with the pore former (FIG. 10A) appeared much more porousand the pores were very uniform.

The unsupported cordierite membrane was made with use of the samecordierite slurry for supported membrane. The same procedure was used asin Example 1. It was fired together with the supported membrane at 1150°C. for 2 h.

FIG. 11 shows the pore size distribution of the cordierite membraneswith Multilobe™ 400, as measured by Mercury porosimetry. The porositywas 48% and median pore size d50 was 0.38 um. The pore size distributionis narrow with the value of (d90−d10)/d50 of 0.77.

In one set of embodiments, a method is disclosed herein for making aporous inorganic membrane comprising the steps of mixing an inorganicmaterial, an acrylic emulsionorganic polymer particles and a solvent toform a slurry, wherein the acrylic emulsion comprises acrylic particles,the particles being non-spherical; distributing the slurry onto asurface; drying the slurry to remove the solvent; and firing the driedslurry to produce the porous inorganic membrane. In some embodiments,the inorganic material comprises alumina, silica, zeolite, orcombinations thereof. In some embodiments, the organic polymer particlescomprise acrylic; in some of these embodiments, the acrylic emulsioncomprises from about 20% to about 60% of the volume of the non-solventmaterials in the slurry. In some embodiments, the surface is a poroussupport and the slurry is distributed on the porous support to form acoating on the porous support; in some of these embodiments, the poroussupport comprises a ceramic porous support. In some embodiments, theporous inorganic membrane has a thickness of from about 0.5 micron toabout 30 microns. In some embodiments, the porous inorganic membrane hasa thickness of from about 1 micron to about 10 microns. In someembodiments, the drying of the slurry comprises drying the slurry isdried at a temperature of from about 25° C. to about 120° C. In someembodiments, the drying of the slurry comprises drying the slurry isdried in an environment of air or N2 at a humidity of from about 60% toabout 90%. In some embodiments, the dried slurry is fired for about 20hours to about 45 hours at a temperature of about 1100° C. to about1400° C. In some embodiments, the porous inorganic membrane has aporosity of from about 30% to about 55%. In some embodiments, the porousinorganic membrane has a pore size distribution as measured by mercuryporosimetry comprising a mono-modal distribution wherein (d90−d10)/d50is less than about 2 (wherein the pores having a size of d90 or lesscomprise about 90% of the total pore volume, the pores having a size ofd50 or less comprise about 50% of the total pore volume and the poreshaving a size of d10 or less comprise about 10% of the total porevolume). In some embodiments, the solvent is an aqueous solvent.

In another aspect, a method is disclosed herein for producing a poroussupport with a porous inorganic coating comprising the steps of: mixingan inorganic material, an acrylic emulsion and a solvent to form aslurry, wherein the acrylic emulsion comprises acrylic particles, theparticles being non-spherical; coating the porous support with theslurry; drying the slurry on the porous support to remove the solvent;and firing the dried slurry on the porous support to produce the poroussupport with the porous inorganic coating. In some embodiments, theinorganic material comprises alumina. In some embodiments, the porousinorganic membrane has a thickness of from about 0.5 micron to about 30microns. In some embodiments, the porous inorganic membrane has athickness of from about 1 micron to about 10 microns. In someembodiments, the acrylic emulsion comprises from about 20% to about 60%of the volume of the non-solvent materials in the slurry. In someembodiments, the porous support is in the form of a honeycomb monolith.In some embodiments, the porous support comprises a ceramic comprisingcordierite, alpha-alumina, mullite, aluminum titinate, titania,zirconia, ceria or combinations thereof. In some embodiments, the slurryfurther comprises a dispersant, a binder, an anti-cracking agent, ananti-foaming agent, or combinations thereof. A porous support with aporous inorganic coating produced by this method is also disclosedherein; in some embodiments, the porous inorganic coating comprises aporosity of from about 30% to about 65% with a median pore size of fromabout 0.01 micron to about 10 microns; in some embodiments, the porousinorganic membrane has a pore size distribution as measured by mercuryporosimetry comprising a mono-modal distribution wherein (d90−d10)/d50is less than about 2 and the pores having a size of d90 or less compriseabout 90% of the total pore volume, the pores having a size of d50 orless comprise about 50% of the total pore volume and the pores having asize of d10 or less comprise about 10% of the total pore volume.

In another aspect, a substrate with a porous inorganic membrane disposedon the substrate is disclosed herein, the inorganic membrane having anaverage thickness of from about 0.5 micron to about 30 microns, and insome embodiments from about 1 micron to about 10 microns, a porosity offrom about 30% to about 65%, a median pore size (d50) of from about 0.01micron to about 1 micron, and a value of (d90−d10)/d50 less than about2, as measured by mercury porosimetry. In some embodiments, thesubstrate is an inorganic porous support.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for making a porous inorganic membrane comprising the stepsof: mixing an inorganic material, organic polymer particles and asolvent to form a slurry, the particles being non-spherical;distributing the slurry onto a surface; drying the slurry to remove thesolvent; and firing the dried slurry to produce the porous inorganicmembrane.
 2. The method of claim 1 wherein the inorganic materialcomprises alumina, silica, zeolite, or combinations thereof.
 3. Themethod of claim 1 wherein the organic polymer particles compriseacrylic.
 4. The method of claim 3 wherein the acrylic comprises fromabout 20% to about 60% of the volume of the non-solvent materials in theslurry.
 5. The method of claim 1 wherein the surface is a porous supportand the slurry is distributed on the porous support to form a coating onthe porous support.
 6. The method of claim 5 wherein the porous supportcomprises a ceramic porous support.
 7. The method of claim 1 wherein theporous inorganic membrane has a thickness of from about 1 micron toabout 10 microns.
 8. The method of claim 1 wherein the drying of theslurry comprises drying the slurry at a temperature of from about 25° C.to about 120° C.
 9. The method of claim 8 wherein the drying of theslurry comprises drying the slurry in an environment of air or N₂ at ahumidity of from about 60% to about 90%.
 10. The method of claim 1wherein the dried slurry is fired for about 20 hours to about 45 hoursat a temperature of about 1100° C. to about 1400° C.
 11. The method ofclaim 1 wherein the porous inorganic membrane has a porosity of fromabout 30% to about 55%.
 12. The method of claim 1 wherein the porousinorganic membrane has a pore size distribution as measured by mercuryporosimetry comprising a mono-modal distribution wherein (d90−d10)/d50is less than about 2 and the pores having a size of d90 or less compriseabout 90% of the total pore volume, the pores having a size of d50 orless comprise about 50% of the total pore volume and the pores having asize of d10 or less comprise about 10% of the total pore volume.
 13. Themethod of claim 1 wherein the solvent is an aqueous solvent.
 14. Amethod for producing a porous support with a porous inorganic coatingcomprising the steps of: mixing an inorganic material, an acrylicemulsion and a solvent to form a slurry, wherein the acrylic emulsioncomprises acrylic particles, the particles being non-spherical; coatingthe porous support with the slurry; drying the slurry on the poroussupport to remove the solvent; and firing the dried slurry on the poroussupport to produce the porous support with the porous inorganic coating.15. The method of claim 14 wherein the inorganic material comprisesalumina.
 16. The method of claim 14 wherein the porous inorganicmembrane has a thickness of from about 1 micron to about 10 microns. 17.The method of claim 14 wherein the acrylic emulsion comprises from about20% to about 60% of the volume of the non-solvent materials in theslurry.
 18. The method of claim 14 wherein the porous support is in theform of a honeycomb monolith.
 19. The method of claim 14 wherein theporous support comprises a ceramic comprising cordierite, alpha-alumina,mullite, aluminum titinate, titania, zirconia, ceria or combinationsthereof.
 20. The method of claim 14 wherein the slurry further comprisesa dispersant, a binder, an anti-cracking agent, an anti-foaming agent,or combinations thereof.
 21. A porous support with a porous inorganiccoating produced by the method of claim
 13. 22. The porous support witha porous inorganic coating of claim 21 wherein the porous inorganiccoating comprises a porosity of from about 30% to about 65% with amedian pore size of from about 0.01 micron to about 1 micron.
 23. Theporous support with a porous inorganic coating of claim 21 wherein theporous inorganic membrane has a pore size distribution as measured bymercury porosimetry comprising a mono-modal distribution wherein(d90−d10)/d50 is less than about 2 and the pores having a size of d90 orless comprise about 90% of the total pore volume, the pores having asize of d50 or less comprise about 50% of the total pore volume and thepores having a size of d10 or less comprise about 10% of the total porevolume.
 24. A substrate with a porous inorganic membrane disposed on thesubstrate, the inorganic membrane having an average thickness of fromabout 0.5 micron to about 30 microns, a porosity of from about 30% toabout 65%, a median pore size (d50) of from about 0.01 micron to about 1micron, and a value of (d90−d10)/d50 less than about 2, as measured bymercury porosimetry.
 25. The substrate of claim 24 wherein the substrateis an inorganic porous support.
 26. The substrate of claim 24 whereinthe inorganic membrane has an average thickness of from about 0.1 micronto about 10 microns.